linux-kernel - Re: [PATCH 3/3] dcache: account external names as indirectly reclaimable memory

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Message-ID: <1475594b-c1ad-9625-7aeb-ad8ad385b793@suse.cz>
Date:   Mon, 16 Apr 2018 14:06:21 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Michal Hocko <mhocko@...nel.org>,
        Johannes Weiner <hannes@...xchg.org>
Cc:     Minchan Kim <minchan@...nel.org>, Roman Gushchin <guro@...com>,
        linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel-team@...com
Subject: Re: [PATCH 3/3] dcache: account external names as indirectly
 reclaimable memory

On 04/16/2018 01:41 PM, Michal Hocko wrote:
> On Fri 13-04-18 10:37:16, Johannes Weiner wrote:
>> On Fri, Apr 13, 2018 at 04:28:21PM +0200, Michal Hocko wrote:
>>> On Fri 13-04-18 16:20:00, Vlastimil Babka wrote:
>>>> We would need kmalloc-reclaimable-X variants. It could be worth it,
>>>> especially if we find more similar usages. I suspect they would be more
>>>> useful than the existing dma-kmalloc-X :)
>>>
>>> I am still not sure why __GFP_RECLAIMABLE cannot be made work as
>>> expected and account slab pages as SLAB_RECLAIMABLE
>>
>> Can you outline how this would work without separate caches?
> 
> I thought that the cache would only maintain two sets of slab pages
> depending on the allocation reuquests. I am pretty sure there will be
> other details to iron out and

For example the percpu (and other) array caches...

> maybe it will turn out that such a large
> portion of the chache would need to duplicate the state that a
> completely new cache would be more reasonable.

I'm afraid that's the case, yes.

> Is this worth exploring
> at least? I mean something like this should help with the fragmentation
> already AFAIU. Accounting would be just free on top.

Yep. It could be also CONFIG_urable so smaller systems don't need to
deal with the memory overhead of this.

So do we put it on LSF/MM agenda?